Journal Article

Bioconversion of tyrosol into hydroxytyrosol and 3,4-dihydroxyphenylacetic acid under hypersaline conditions by the new <i>Halomonas</i> sp. strain HTB24

Pierre-Pol Liebgott, Marc Labat, Laurence Casalot, Agnès Amouric and Jean Lorquin

in FEMS Microbiology Letters

Volume 276, issue 1, pages 26-33
Published in print November 2007 |
Published online August 2007 | e-ISSN: 1574-6968 | DOI: https://dx.doi.org/10.1111/j.1574-6968.2007.00896.x

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Abstract

This paper reports the characterization of a Halomonas sp. strain (named HTB24) isolated from olive-mill wastewater and capable of transforming tyrosol into hydroxytyrosol (HT) and 3,4-dihydroxyphenylacetic acid (DHPA) in hypersaline conditions. This is the first time that a halophile has been shown to perform such reactions. The potent natural antioxidant HT was obtained through a C3 hydroxylation on the ring cycle, whereas DHPA was synthesized via the 4-hydroxyphenylacetic acid (HPA) pathway, which has been well described from other bacterial sources. HT was produced first, and then DHPA was detected in the medium accompanied by traces of HPA. HPA involved another pathway resulting from the activity of an aryl-dehydrogenase, which is suggested to be responsible for both tyrosol and hydroxytyrosol oxidation. Maximal HT content (2.30 mM) and maximal DHPA (5.15±0.42 mM) were obtained from a culture inoculated in the presence of 20 mM tyrosol and 0.5 g L−1 yeast extract. Following this, DHPA was quickly degraded into 5-carboxymethyl-2-hydroxymuconic semialdehyde by a 2,3-dioxygenase, finally resulting in succinate and pyruvate. Phylogenetic analysis of the 16S rRNA gene revealed that this isolate was a member of the genus Halomonas. Strain HTB24, with a G+C content of 55.3 mol%, is closely related to Halomonas neptunia DSM 15720T, ‘Halomonas alkaliantarctica’ DSM 15686T and Halomonas boliviensis DSM 15516T.

Keywords: Halomonas; tyrosol; hydroxytyrosol; 3,4-dihydroxyphenylacetic acid

Journal Article.  4580 words.  Illustrated.

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